The systemic immune response and central nervous system (CNS) events occurring during acute HIV likely set the stage for chronic HIV-related CNS injury and the establishment of CNS-relevant HIV reservoirs. Just as the earliest systemic features such as peak plasma HIV RNA, level of T-cell activation, and early loss of CD4 cells are crucial determinants of HIV disease trajectory, CNS processes initiated during the earliest stages may critically inform the establishment of a CNS-relevant viral reservoirs, CNS compartmentalized virus, the hosts' ability to control CNS virus, and the long-term CNS consequences of infection. Logistical challenges have lead to heavy reliance on animal data to define the likely CNS events during acute HIV. In this application, we extend existing partnerships with US Army studies underway in Thailand to define these earliest events in humans and determine factors that influence long-term CNS outcomes. This application proposes to provide intensive CNS characterization for 60 Thai subjects enrolled during acute HIV (< 1 month after exposure). In our schema, one-half of subjects will begin HAART immediately after initial assessments for a fixed 18-month course. We will longitudinally characterize CNS clinical events, neurological, neuropsychological, and psychiatric factors, multimodal magnetic resonance imaging, CSF immunology and compartment specific full-genome HIV sequencing to determine how the events that occur in acute HIV impact chronic HIV CNS disorders. We will also determine CNS founder and established viruses and determine if early HAART intervention impacts these relationships. The parent studies include extensive systemic immunological and virological characterization allowing us to determine if the earliest systemic events impact long-term CNS outcomes.